The concept of preparing silicon carbide ceramic materials or silicon carbide-containing ceramics from silicon carbide ceramic materials is not new. As applied to the preparation of silicon carbide-containing ceramics from the degradation of polymers, any number of published articles or issued patents have appeared.
Yajima in U.S. Pat. No. 4,052,430, issued Oct. 4, 1977, has described the preparation of polycarbosilanes prepared by pyrolyzing the polysilanes generated by the reaction of sodium or lithium metal with dimethyldichlorosilane. These polycarbosilanes can be heated to yield beta-silicon carbide.
West and Maszdiazni reported in the 22nd AFOSR Chemistry Program Review FY77, R. W. Heffner ed. March (1978), that a polymer, made by reacting dimethyldichlorosilane with methylphenyldichlorosilane and an alkali metal, could be fired at high temperatures to yield whiskers of beta-silicon carbide.
Verbeek has shown in U.S. Pat. No. 3,853,567, the preparation of a mixed ceramic of silicon carbide and silicon nitride by pyrolyzing a polysilazane. In addition, Verbeek has prepared a polycarbosilane suitable for molding by heating organosilicon polymers optionally mixed with silicon dioxide or organic polymers at a temperature between 400.degree. and 1200.degree. C.
Rice et al., in U.S. Pat. No. 4,097,794 issued June 27, 1978, have suggested that almost anything containing silicon can be pyrolyzed to give a ceramic material.
Baney, in U.S. Pat. application Ser. No. 910,247, filed May 30, 1978, now abandoned, and continued as a continuation-in-part, Ser. No. 024,137, filed Mar. 26, 1979, now abandoned and continued as a continuation-in-part of Ser. No. 135,567, filed Mar. 31, 1980 disclosed a methylhalopolysilane which can be fired at 1200.degree. C. or higher to yield fine grain beta-silicon carbide. The yields and handling characteristics of these latter polysilanes were enhanced over the prior materials.
Mention should be made of recent Japanese patent publications Nos. 80500/78 and 101099/78 in the name of Takamizawa et al. These publications deal with polymers made from methylchlorodisilanes but no mention is made of the yields of ceramic materials generated by the decomposition of the polysilanes. Recent publications by Nakamura (Japanese Kokais Nos. 79/114600 and 79/83098) suggest that the preparation of silicon carbide precursor polymers having a silicon carbon (-Si-C-Si-) backbone are prepared by heating organosilicon compounds (including (CH.sub.3).sub.3 SiSi(CH.sub.3).sub.2 Cl) in the presence of B, Al, Si, Ge, Sn and Pb compounds or HI and its salts, at high temperatures.
It has now been determined that high yields of silicon carbide ceramic materials and silicon carbide-containing ceramics can be obtained from the methods and the new materials of the instant invention.